The present invention relates, in general, to data compression and, more particularly, to a method for encoding and decoding still video frames and a sequence of frames of digitized motion picture video data.
Methods for compressing, or encoding, digitized video data have been known in the art for some time. One well-known method for compressing individual digitized images is the JPEG (Joint Photographic Expert Group) method. A well-known method for encoding a sequence of frames of digitized motion picture video data is the MPEG (Motion Picture Expert Group) method. While the MPEG compression method generally provides visually acceptable results with respect to the compressed and decompressed video image, relatively sophisticated hardware is required in order to perform the compression and decompression methods. In particular, the MPEG standard specifies the use of a discrete cosine transformation (DCT) to perform data compression, as well as an inverse discrete cosine transformation (IDCT) to perform the data decompression method. The DCT and IDCT transformations each require a significant number of multiply-accumulate operations, which, in turn, requires relatively complex dedicated hardware, or relatively high speed digital signal processors or microprocessors, to perform the required method.
Another prior art method for encoding individual video frames is the block truncation coding (BTC) method. A flow diagram of the prior art BTC method is shown in FIG. 1 of the drawings. In the BTC method, each pixel of an image is subdivided into its red, green, and blue color components. Each frame is subdivided into square blocks and then further subdivided into respective red, green, and blue component sub-blocks, each containing a single color component for pixels in the associated block. Two quantization intensities, (an upper intensity and a lower intensity), are determined for each sub-block. The red, green, and blue color components of each pixel are then quantized so as to be represented by either the upper or lower quantization intensity for its associated sub-block. In this manner, a video frame may be represented by three bit-mapped matrices, having three bits for each pixel in the corresponding video frame, plus a plurality of upper and lower quantization values.
While this prior art BTC coding method provides for satisfactory compression and decompression of individual images, a relatively large number of bits are required to represent the image in encoded form. Moreover, relatively sophisticated encoding and decoding hardware, or a relatively high level of processing speed, is required in order to calculate the quantization values.
In addition, the prior art block truncation coding method is directed to the encoding and decoding of individual images, and is not optimized for sequences of digitized motion picture video data. For example, the prior art BTC compression and decompression methods do not take advantage of the similarities which often occur within the content of adjacent, related frames of digitized motion picture video data.
Accordingly, it is an object of the present invention to provide a method for encoding and subsequently decoding a sequence of digitized motion picture video data, wherein a relatively small number of bits of information is required in order to represent the frames of video data in compressed, encoded form.
It is another object of the present invention to provide a method for compressing and subsequently decompressing frames of digitized motion picture video data, wherein interframe analysis is employed to take advantage of similarities in adjacent video frames.
It is yet another object of the present invention to provide a method for encoding and subsequently decoding still video frames, wherein a relatively small number of bits of information is required in order to represent the still frames in compressed, encoded form.
These and other objects and features of the present invention will become apparent in light of the present specification, claims, and drawings.